Effects Of Systematic Changes Research Articles

Humidity influence on the adhesion of biomimetic fibrillar surfaces

Abstract The recent interest in fibrillar biological attachment systems, as found in the gecko, has led to the development of micropatterned elastomer adhesion surfaces. All reported studies have been performed at ambient humidity neglecting its possible influence on adhesion. The present paper investigates, for the first time, the effect of systematic changes in ambient humidity from 2 to 90 %. Adhesion measurements were performed on PDMS (Sylgard 184) surfaces possessing micropillars with flat-ended and hemispherical contact shape. The pillar radius was varied between 2.5 and 25 μm; the pillar aspect ratio was kept at 1. While the adhesion of a flat sample was not affected by humidity, we found that pillar size and shape influenced the sensitivity to humidity changes: Thinner pillars, with higher pull-off forces in the dry state, exhibited decreasing adhesion values, by up to 35 %, with increasing humidity. The effect was stronger for the hemispherical tip shape, where the positive effect of finer pillars was even reversed. Possible explanations for these effects, which may lower the reliability of biomimetic adhesion devices in the presence of humidity, are given.

Implications of global climate change for snowmelt hydrology in the twenty‐first century

AbstractFor most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid‐twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow‐affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm‐season runoff in many mid‐ to high‐latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high‐latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt‐derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd.

Interface Effects on the Quasi-Static and Impact Toughness of Discontinuously Reinforced Aluminum Laminates

Trilayer laminates consisting of two layers of aluminum alloy 7093 surrounding one layer of 7093/SiC/15p were produced via two roll-bonding techniques as well as by adhesive bonding. The effects of systematic changes in interface characteristics (i.e., weak bond via roll bonding with a thin ductile interlayer material, stronger bond via roll bonding without a thin ductile interlayer, and strongest bond via adhesive bonding with a semibrittle material) on the subsequent laminate toughness was studied. The fracture resistance of the laminates and the constituent materials was examined via instrumented Charpy notched impact testing in the crack-arrester orientation as well as by fracture-toughness testing of bend bars tested in the crack-divider and the crack-arrester orientations. The notched impact resistance of the trilayer crack-arrester laminates was found to be greater than both monolithic 7093/SiC/15p and 7093 samples of similar global thickness. The laminated structure promoted crack arrest, deflection, and large-scale deformation of the unreinforced layers, producing R-curve behavior. The tendency for interface delamination was predicted and confirmed based on recent mechanics-based analyses. The trilayer laminate structures tested in the crack-divider orientation exhibited a greater R-curve than either of the 7093/SiC/15p or 7093 samples tested at similar global thickness. Both types of roll-bonded laminates (i.e., stronger interface and weak interface containing a thin metal interlayer) exhibited a greater enhancement in Charpy impact toughness and mode I fracture toughness than did the adhesively bonded (i.e., semibrittle interface) laminates. These relative improvements in toughness were rationalized by estimating the contributions to energy absorption by the delamination and crack bridging in these systems and by the effects of the interface type on these processes. These results are generally relevant to the performance of these materials under impact and under certain blast loading and penetration situations.

Microstructural effects on tension and fatigue behavior of Cu–15Ni–8Sn sheet

The effects of systematic changes in microstructure/heat treatment on the mechanical behavior of Cu–15Ni–8Sn (Pfinodal ®) were evaluated in uniaxial tension and in cyclic strain-controlled fatigue with the use of a modified GE Flex Tester operated to provide fully reversed bending fatigue. The magnitude of cyclic strains was controlled via the use of different diameter mandrels. Smaller diameter mandrels produced higher values of cyclic strain and lower fatigue life. Multiple samples were tested and fracture surfaces were analyzed via scanning electron microscopy. The fatigue results were analyzed via a Coffin–Manson–Basquin approach and compared to fatigue data obtained from the literature, where testing was conducted on similar materials. Significant effects of cold work and heat treatment on both the tension and fatigue behavior were obtained and rationalized based on the mechanisms of failure, revealed by SEM, for this system.

Controlling structure in associating polymer-surfactant mixtures

Abstract Structures of concentrated mixtures of associating polymer-surfactant mixtures are important in many technical applications. Yet an in-depth understanding of how molecular parameters affect these structures is lacking. We here summarize the results of ongoing work using a novel simplified approach to the study of associating oppositely charged polymer-surfactant mixtures, introducing a minimum number of components to the various mixtures. The results illustrate the relations between systems with and without polyions, as well as effects of systematic changes of parameters such as surfactant chain length, polyion length, polyion charge density, and the charge density of the surfactant aggregate.

Effect of Systematic Changes of Ti and Hf Si-oxynitride Alloys by Nitrogen Incorporation as a Bond Constraint on Electrical and Material Properties

AbstractWe have investigated the effect of Si3N4 content in (Ti(Hf)O2)x(Si3N4)y(SiO2)1-x-y pseudo-ternary alloys by tracking systematic changes of electrical properties, including electrically active defects. Results from Soft x-ray photoelectron spectroscopy (SXPS) studies indicate no detectable hole traps for Ti/Hf Si oxynitrides with Si3N4 content >35%; these alloys have equal concentrations of Ti(Hf)O2 and SiO2, ~30-32%, and additionally are stable for annealing in Ar ambients to temperatures of 1100°C. Derivative near edge x-ray absorption spectroscopy (NEXAS) comparisons for the O K1 edges of TiO2 and optimized Ti Si oxynitride alloys provides a significantly reduced average crystal field d-state splitting from 1.9 to 1.6eV, as well as decreased electron trapping, and is correlated with a four-fold coordination of Ti in the Ti Si oxynitride alloys. The flat band voltage shift with varying frequency from 10 kHz to 1MHz in these alloys is less than 12 mV and the compositional dependence of current-voltage characteristics on Si3N4 composition results in the lowest leakage current at a Si3N4 content of ~40 % with the smallest equivalent oxide thickness (EOT) as well. Based on these studies, Transition Metal (TM) Si oxynitride alloys are anticipated to yield EOT <1 nm for scaled CMOS devises.

Nonstandardized Assessment Approaches for Individuals with Traumatic Brain Injuries

Nonstandardized assessment procedures serve a variety of purposes, including determining competencies in domains for which there are no standardized tests, describing performance in the context of real-world settings and activities, and exploring the effects of systematic changes in communication and cognitive demands and partner supports. This article reviews evidence on the use of nonstandardized procedures for the assessment of individuals with traumatic brain injury and offers recommendations for the use of the procedures that are supported by the available evidence.

Synthesis of biocompatible segmented polyurethanes from aliphatic diisocyanates and diurea diol chain extenders

Many polyurethane elastomers display excellent mechanical properties and adequate biocompatibility. However, many medical-grade polyurethanes are prepared from aromatic diisocyanates and can degrade in vivo to carcinogenic aromatic diamines, although the question of whether the concentrations of these harmful degradation products attain physiologically relevant levels is currently unresolved and strongly debated. It is therefore desirable to synthesize new medical-grade polyurethanes from less toxic aliphatic diisocyanates. In this paper, biocompatible segmented polyurethane elastomers were synthesized from aliphatic diisocyanates (1,4-diisocyanatobutane (BDI) and lysine methyl ester diisocyanate (LDI)), novel diurea diol chain extenders based on tyrosine and tyramine, and a model poly(ethylene glycol) (PEG) diol soft segment. The objectives were to design a hard segment similar in structure to that of MDI-based polyurethanes and also investigate the effects of systematic changes in structure on mechanical and biological properties. The non-branched, symmetric polyurethane prepared from BDI and a tyramine-based chain extender had the highest modulus at 37 °C. Introduction of symmetric short-chain branches (SCBs) incorporated in the tyrosine-based chain extender lowered the modulus by an order of magnitude. Polyurethanes prepared from LDI were soft polymers that had a still lower modulus due to the asymmetric SCBs that hindered hard segment packing. Polyurethanes prepared from tyramine and tyrosine chain extenders thermally degraded at temperatures ranging from 110 to 150 °C, which are lower than that reported previously for phenyl urethanes. All four polyurethanes supported the attachment, proliferation, and high viability of MG-63 human osteoblast-like cells in vitro. Therefore, the non-cytotoxic chemistry of these polyurethanes make them good candidates for further development as biomedical implants.

Chemically Induced Destabilization of Water-in-Crude Oil Emulsions

The effect of systematic changes in the structure of chemicals commonly used in demulsification operations (alkylphenol polyalkoxylated resins and polyurethanes) on the stability and properties of brine-in-crude oil emulsions was assessed experimentally. The relative rates of water separation were characterized via bottle tests and rheometry. Equilibrium interfacial tensions were also measured. Transient changes in drop size distributions were quantified using nuclear magnetic resonance. The phenolic resins promoted coalescence of droplets. Optimum performance was obtained with resins exhibiting intermediate hydrophilicity in a manner consistent with the condition of least emulsion stability for conventional oil−water−surfactant systems. In contrast, polyurethanes promoted flocculation but only slow coalescence. The performance of polyurethanes improved with increase of molecular weight. Phenolic resins and polyurethanes acted synergistically when added simultaneously, rendering water separation rates sig...

Langmuir and Langmuir−Blodgett Films of Amphiphilic Bistable Rotaxanes

A series of amphiphilic bistable [2]rotaxanes--in which a ring-shaped component, the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), has been assembled around two recognition sites, a tetrathia-fulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) ring system, situated apart at different strategic locations within the central polyether section of an amphiphilic dumbbell component that is terminated by a hydrophobic tetraarylmethane-based stopper (near the TTF unit) at one end and by a hydrophilic tetraarylmethane-based stopper (near the DNP ring system) at the other end--has been designed and synthesized. The effects of systematic changes in the constitutions of the three ethylene glycol tails (diethylene or tetraethylene glycol) and end groups (hydroxyl or methoxyl functions) attached to the hydrophilic stoppers on Langmuir film balance and surface rheology experiments at 20 degreesC were examined to determine the monolayer stabilities and co-conformations of the [2] rotaxanes and their free dumbbell counterparts. These experiments allow us to propose a model for the rotaxane's structures at different surface pressures. All the [2]rotaxanes form stable Langmuir films. These films typically pass from a liquid-expanded region to a liquid-condensed region. The transition between the two regions was either directly observed or ascertained using film stability experiments. Film balance and surface rheology experiments showed that the addition of the tetracationic cyclophane component and hydroxyl end groups markedly increased the stabilities and viscoelasticity of the films.

On the structural significance of the linkage region constituents of N-glycoproteins: an X-ray crystallographic investigation using models and analogs

The linkage region constituents, namely, 2-acetamido-2-deoxy-β- d-glucopyranose and asparagine are conserved in the N-glycoproteins of all the eukaryotes. The present work is aimed at understanding the reasons for the occurrence of GlcNAc and Asn as the linkage region constituents. A total of six sugar amides have been designed as models and analogs of the linkage region and their crystal structures have been solved. This is the first report on the X-ray crystallographic investigation of the effect of systematic changes in the linkage sugar as well as its aglycon moiety on the N-glycosidic torsion, ψ N (O5–C1–N1–C1 ′). This also forms the first report on the crystal structure of a model of l-RhaβAsn, a variant linkage found in the surface layer glycoprotein of Bacillus stearothermophillus. Among the models and analogs examined, the acetamido derivatives of Man and Xyl, the linkage sugars of O-glycoproteins, show a ψ N value of −114.5° and −121.2°, respectively, deviating maximum from the value of −89.8° reported for the model compound GlcNAcβNHAc. The l-Rha and Gal derivatives also show noticeable deviations. The ψ N values, −89.5° and −91.0°, of the propionamide derivatives of Glc and GlcNAc (analogs of GlcβGln and GlcNAcβGln, respectively) agree well with those (−93.8° and −89.8°) reported for their corresponding acetamide derivatives suggesting Gln could serve as well as Asn as the linkage region amino acid. However, the rotational freedom about the additional C–C bond would lead to altered rigidity of the linkage region. An analysis of packing reveals that the molecular assembly of these compounds is driven by different infinite and finite chains of hydrogen bonds. The double pillaring of hydrogen bonds involving the amide groups at C1 and C2 is seen as a unique packing feature characteristic of β-1- N-acyl derivatives of GlcNAc. Based on the findings of the present study, it is speculated that the linkage region constituents of the eukaryotic N-glycoproteins appear to fulfill three essential structural requirements: rigidity, planarity, and linearity and these are met by the trisaccharide core and Asn at the linkage region.

Effect of composition on the properties of glasses in the K 2O–BaO–MgO–SiO 2–Al 2O 3–B 2O 3–MgF 2 system

Twenty five glasses in the(1− Z)BaO:ZK 2O:(6− X)MgO: XMgF 2:(3− Q)Al 2O 3: QB 2O 3:8SiO 2 system have been prepared and the effect of systematic changes in composition ( Z=0, 0.25, 0.5, 0.75 and 1.0, X=2, 2.5 and 3.0 and Q=0, 0.5 and 1) on molar volume (MV), fractional glass compactness (C), microhardness (μ H V), glass transition temperature ( T g mid ) and coefficient of thermal expansion ( α) determined. As potassium is substituted for barium (increasing Z), increases in MV and α, and decreases in C, μ H V and T g mid arise which are attributed to the replacement of O NB–Ba–O NB ionic bridges by two O NB–K terminations (O NB = non-bridging oxygen). When fluorine is substituted for oxygen, reductions in μ H v and T g mid and increases in MV and α values occur. These property changes occur because of reduced crosslink densities associated with the replacement of ≡Al–O–Si≡ crosslinks by ≡Al–F terminations. In general, the substitution of aluminium by boron results in decreases in MV, μ H V and T g mid values and increases in α values. These effects are attributed to boron assuming a tri-coordinated state in the glass, giving rise to reduced crosslink densities, together with the release of modifier cations (Mg, K and Ba) from their charge balancing role for four-coordinated aluminiums leaving them free to cause greater network disruption.

Reassessment of H-reflex recovery curve using the double stimulation procedure.

We conducted two types of experiments to assess the validity of the H-reflex recovery test, using double stimulation to test soleus motoneuron pool excitability in healthy and spastic subjects. One type dealt with the mechanical effect of the conditioning H reflex on the ankle joint; the other type with the effect of change in reflex size. The mechanical effect was tested both with the ankle joint fixed (FX) and free to move (FR). Differences between FX and FR conditions commenced with relaxation of soleus muscle contraction by the conditioning H reflex. In the FR condition, abrupt facilitation occurred, and changed to marked depression. We conclude that specific facilitation and inhibition in the FR condition were secondary effects of group Ia inflows caused by the ankle extensor muscle stretching on relaxation. In some spastic patients as well as in controls, facilitation due to the mechanical effect in the FR condition was observed despite the FX condition. The effects of systematic changes on soleus H-reflex size were investigated at conditioning-test intervals of 80 ms, so as to avoid mechanical effects. When conditioning and test reflexes were the same size, the amount of recovery increased as the H-reflex size increased. Comparison of the relation between amount of recovery and H-reflex size, expressed as a percentage of Mmax, showed no significant difference between the two groups. We speculate that the stronger recovery of spasticity mentioned in previous literature may have resulted from the fact that relatively greater H reflexes were tested in those studies. In conclusion, the present study indicates that double stimulation is not appropriate for assessing spinal motoneuron pool "excitability increase" in spasticity.

Finite Difference Maxwell Solver to Study Geometric Shape Effects on Radar Signature

The development and application of a e nite difference time-domain solver for Maxwell’ s equations are presented. The work described here is the result of a research effort aimed at developing an accurate and efe cient numerical method capable of simulating electromagnetic scattering from three-dimensional arbitrarily shaped objects to predict their radar cross sections (RCS). The e nite difference formulation is presented and the accuracy of the Maxwell solver is demonstrated for several test cases. The capability of the Maxwell solver as a design and analysis tool is illustrated through a parametric study that examines the effects of systematic changes in the shape of aircraft wings on their RCS. The results indicate that for head-on radar illumination, a signie cant reduction in the RCS of a wing can be achieved by sweeping its leading edge and varying its spanwise thickness.

Ultimatums in two-person bargaining with one-sided uncertainty: Demand games

The demand game is a noncooperative two-person ultimatum game with one-sided uncertainty in which the Sender knows the value of the shared surplus (pie) but the Receiver only knows its probability distribution (Mitzkewitz and Nagel, 1993). We study experimentally the effects of systematic changes in the variability of the pie distribution on the Sender's proposals and Receiver's (binary) responses. In accordance with a behavioral theory that we propose, we find that 1. (i) the Sender's proportional share of the pie increases as the Receiver's uncertainty about the pie increases, and 2. (ii) for a given pie distribution, the Sender's proportional share decreases as the actual pie size increases.

Validation of input data for trained neural-nets

The validation of input-data samples is a very important issue for neural-net applications if high precision is required. The aim is to make sure that a neural net properly trained on one data sample gives reliable results for another. Using the search for the standard Higgs boson at LEP-200 as an example, the effect of systematic changes in the input data is studied in detail for feed-forward nets. Several methods for recognizing significant differences between the training-data sample and a test-data sample are presented.

Systematic comparison of data-processing options for kinetic-based single-component determinations of non-catalysts: Part 2. One-rate, two-point/fixed-time, two-rate, three-point/fixed-time options

This paper describes and compares performance characteristics of four data-processing options for kinetic-based determinations. Options compared are two-point/fixed-time, one-rate, three-point/fixed-time and two-rate methods. Features evaluated are the effects of systematic changes in variables such as rate constants and reaction order as well as different levels of random noise. Both simulated and experimental data are used to evaluate effects of systematic changes in rate constants and simulated data are used to evaluate effects of random noise and systematic deviations from first-order behavior. All the options appear to be relatively independent of small changes (±0.1) in reaction order. The two-point/fixed-time and one-rate options have no inherent ability to reject effects of systematic changes in rate constants but optimum conditions can be identified that reduce effects of such changes. The latter two methods have the inherent ability to reject effects of systematic changes in rate constants but appear to be more dependent on random noise than the two-point/fixed-time and one-rate options. Application of the optimized two-point/fixed-time and one-rate methods and the three-point/fixed-time and two-rate options to experimental data for uric acid demonstrate 40- to 100-fold improvements in ruggedness for changes in the rate constant relative to non-optimized two-point/fixed-time and one-rate methods.

Polymeric Sorbents for Bile Acids. III. Hydrophilic and Hydrophobic Models 0f Cholestyramine

Abstract A study is presented of the binding of glycocholate bile salt anions by crosslinked polymeric beads consisting of either an acrylamide or a Merrifield resin. Various amine-containing pendant groups have been synthesized onto the functional sites of the backbones of these resins, thus forming bile acid sorbents. Based on the effects of systematic changes in the structure of the functional groups on the sorption isotherms, it is shown that the extent of binding is favored by changes that increase the basicity, especially quaternization. On the other hand, sorption is inhibited by extensive crosslinking. It is concluded that the sorption of glycocholate by these sorbents involves an ion-exchange mechanism.

Effect of reinforcement size and matrix microstructure on the fracture properties of an aluminum metal matrix composite

The effects of systematic changes in reinforcement size and matrix microstructure on the crack initiation and growth toughness of a 7091 aluminum alloy reinforced with SiC particulates were studied. It is shown that changes in matrix microstructure have a significant effect on both initiation and growth toughness. The effect of reinforcement size on these properties is far less marked. These observations have been related to local microstructural parameters and the nature of the distribution of the reinforcement.

The Effect of Hip Position/Configuration on Anaerobic Power and Capacity in Cycling

The purpose of this investigation was to determine the effect of systematic changes in hip position/configuration on cycling peak anaerobic power (AP) and anaerobic capacity (AC). Fourteen male recreational cyclists (ages 21-32 yrs) were tested in four hip positions (25, 50, 75, and 100°), as defined by the angle formed by the seat tube and a vertical line. Rotating the seat to maintain a backrest perpendicular to the ground induced a systematic decrease in hip angle from the 25 to the 100° position. The Wingate anaerobic cycling test was used on a Monark cycle ergometer with a resistance of 85 gm/kg of the subject’s body mass. Repeated-measures MANOVAs and post hoc tests revealed that AP and AC in the 75° hip position were significantly greater than in the 25 or 100° position and that a second-order function best describes the trend in AP and AC with changes in hip position.